Pyrite Penetration Twin
A Pyrite Penetration Twin is a specific type of crystal twinning observed in pyrite (FeS₂), a common iron sulfide mineral.
Crystal twinning in minerals occurs when two or more individual crystals grow together in a symmetrical fashion. In penetration twins, the twin individuals intergrow in such a way that they appear to penetrate each other, often forming complex interlocking geometries.
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| Pyrite Penetration Twin. |
In pyrite, a penetration twin is a distinctive and diagnostic crystallographic habit. These twins commonly form when two cubic pyrite crystals intersect at specific crystallographic angles, often forming a cuboctahedral intergrowth or an interpenetrating cross-shaped geometry. These twins are usually governed by the [111] twin law, where the twinning occurs along the diagonal of the cube face.
Navajun, located in La Rioja, Spain, is famous for its exceptional pyrite specimens, particularly for the high-quality, large penetration twins.
A penetration twin in pyrite occurs when:
Two crystals of pyrite grow together in such a manner that they interpenetrate each other. They share a common crystallographic plane or axis, where their lattices are symmetrically related but not parallel.
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